This invention relates to a fuel injection system for internal combustion engines having an amount of fuel injection to the engine controlled in relation to pressure in an intake pipe and more particularly to an system for measuring precisely the pressure in the intake pipe of the engine to control accurately the amount of fuel injection.
The pressure in the intake pipe of the internal combustion engine consists of average pressure determined by flow resistance and intake air flow according to a throttle valve and a pulsating component of intake pressure produced at every intake stroke of the engine and overlaid on the average pressure. In said type of fuel injection system, a pressure sensor for converting the intake pressure necessary for calculating the amount of fuel injection to electric signals is provided in the intake pipe. To remove the pulsating component of the intake pressure for measuring accurately the average pressure, either a throttle is provided between the intake pipe and the pressure sensor, or a low pass filter is provided between the sensor and an injection time calculating unit.
Though the pulsating component of the intake pressure can be removed by such throttle or low pass filter, a large delay in response to draft change in the average pressure takes place in acceleration or deceleration of the engine. This delay in the response of the average pressure in the acceleration or deceleration produces errors in the amount of fuel injection under such transitory running condition, resulting in the degradation of accelerating ability of the engine and the increase of noxious components of exhaust gas in the acceleration or deceleration.